There is really no difference in the piece of tape in the higher serial numbered models for the light leak fix. I had one of the early models, the light leak was a red herring, it does not affect anything unless you are taking photos in the dark while letting the camera meter (Bad Idea) and having the top lcd light on.
However, prices for used models are high, and there is no warranty. Sellers may have discovered intermittent issues, have hot pixels, or other things that you cannot see during a quick inspection.
I'd rather buy a gray market model with third party insurance than a used one.